This invention relates to a process for decomposing certain halogenated hydrocarbons, particularly polychlorinated biphenyls, using microwave radiation.
Polychlorinated biphenyls (PCBs) have been widely used as insulating materials in electrical equipment, heat exchange liquids, plasticizers and for other industrial applications. It has been determined, however, that PCBs and other polyhalogenated organic compounds are a source of ecological problems including toxic effects on humans, animals, vegetation, soil and air. As a result, the use of PCBs is now banned in many countries including Canada and the U.S. However, safe disposal of waste PCBs still remains a problem due to the very nature of halogenated hydrocarbons, i.e. high stability to chemical and biological degradation.
A number of methods have been proposed to decompose polychlorinated biphenyls and other halogenated hydrocarbons. Some of the methods employ a high temperature treatment and therefore carry the risk of air pollution due to the emission of noxious fumes and vapors to the environment. When heated to a temperature from 300.degree. C. to 900.degree. C. in the presence of air, PCBs produce highly toxic dioxins. Also, incineration as a way to disposal of hazardous chemicals in general has a notable drawback in that it requires substantial energy consumption.
It has been found recently that certain decomposition reactions of halogenated organic compounds can be stimulated by the use of microwaves or other forms of radiation, e.g. UV or solar energy. U.S. Pat. No. 4,345,983 (Wan) teaches a process in which a chlorinated hydrocarbon is brought into contact with iron powder in the presence of high-intensity microwave radiation. U.S. Pat. No. 4,632,742 (Tundo) discloses a method in which an halogenated organic compound is reacted with a mixture of reactants including a polyethylene glycol, a base and a source of free radicals such as a peroxide, a persalt or a metal of high valence. The reaction is carried out in the presence of electric fields, ultrasounds or microwaves.
A combination of UV and microwave radiation as a stimulating factor in the degradation of PCBs has been taught in European patent application Ser. No. 257,170 (Tumiatti). Solar energy has been proposed in U.S. Pat. Nos. 4,432,344 and 4,549,528.
There is still a need for a safe and efficient process for the decomposition of halogenated or polyhalogenated hydrocarbons where the risks associated with high-temperature treatment would be eliminated.